Lately, a superconductor has been used to develop a superconducting bearing which allows a high speed rotation by axially supporting a rotor (rotation axis) in a non-contact state. As shown in FIG. 38, a superconducting bearing first consists of one ring-like permanent magnet 32 which is coaxially disposed on a rotor (rotation axis) 31 having the axis perpendicularly arranged and has both ends along the axial direction of the rotor 31 mutually magnetized in opposite polarities, and a ring-like superconductor 33 disposed to oppose the opposite face of the permanent magnet 32 with a gap therebetween in the direction of the rotating axis (For example, Japanese Patent Application No. 51430/1991). In FIG. 38, 34 represents a circular plate attached to the rotor 31, 35 a permanent magnet comprising the ring-like permanent magnet 32 and the circular plate 34, 36 a circular plate support to which the superconductor 33 is fixed, 37 a superconductor member comprising the superconductor 33 and the circular plate support 36, 38 a cooling case, 39 a temperature control unit, and 40 a refrigerator.
A conventional superconducting bearing is then proposed, to enhance a load capacity and stiffness, to dispose for example two ring magnets 32A, 32B to adjoin each other to increase the surface area of magnets as shown in FIG. 39. And, to further improve a loading force, two ring magnets 32A, 32B are reversely magnetized from the axial direction as shown in FIG. 40. In FIG. 39 and FIG. 40, setting is made to be a=b=30 mm.
However, according to the prior art of the above publication, an integral ring-like permanent magnet which can be used for a small bearing has a drawback of being difficult to be used for a larger bearing in view of the production and magnetization.
Specifically, to form a large-sized bearing, it is necessary to produce an integral ring-like permanent magnet having a large diameter. Generally, a powerful magnet having a large energy product includes rare earth magnets, and an Nd-Fe-B magnet is known as the most powerful rare earth magnet at present. But, since this magnet is produced by a sintering method, a larger making machine and higher pressure are required as its size becomes larger, and the production is limited to an integral ring-like permanent magnet having a diameter of about 100 mm at present. A Pr magnet (Pr-Fe-B-Cu) which is produced by a hot rolling method can be produced into an integral ring-like permanent magnet having a diameter of 100 mm or more. But, even if a ring-like permanent magnet having a large diameter is produced, it is difficult to attach to a circular plate because magnetic force is high. Further, to attach a ring-like permanent magnet having a large diameter, a size becomes excessively large including a magnetized yoke, and it is quite dangerous because of internal breakage of the magnet and breakage of the magnetized yoke due to mechanical energy generated when magnetizing. Besides, it is dangerous to transfer the magnet.
Therefore, the ring-like permanent magnet 32 having a large diameter may be formed by joining a plurality of magnets 41, 41, . . . in the circumferential direction (a direction along the circumference) to form a ring as shown in FIG. 41. But, this ring-like permanent magnet 32 has the nonuniformity of magnetic flux in the revolving direction deteriorated at the joint parts of the magnets 41, 41, . . . causing uneven magnetic flux and a drawback of increasing a loss of revolving energy of the bearing as shown in FIG. 42. And, in case of a ring-like permanent magnet integrally formed in the shape of a ring, there is the same drawback as above in the production because of the presence of uneven magnetic flux.
And, as shown in FIG. 39, when a plurality of ring-like permanent magnets 32A, 32B is coaxially disposed to adjoin each other to enhance magnetic flux density and to obtain high magnetic field intensity, since the directions of magnetic fluxes in individual ring-like permanent magnets 32A, 32B are parallel as shown by arrows in FIG. 39, characteristics of magnetic flux density at a point 2 mm away from the exposed magnet surface are flat at the section W which is a width of both magnets 32A, 32B as shown in FIG. 43, and the absolute quantity of magnetic flux density is only 5 kG (gauss) at a maximum, and magnetic field intensity is limited. The magnetic field intensity of the magnet influences a loading force of the superconducting bearing, and when it is high, a loading force is increased and a heavy fly wheel can be supported, and a load capacity can be increased.
Consequently, this invention aims to provide a superconducting bearing which can improve the uniformity of surface magnetic field density in the circumferential direction by decreasing uneven magnetic flux in the circumferential direction (revolving direction) with a ring-like magnet, can increase magnetic field intensity by the ring magnet, resulting in increasing a loading force so as to be applicable to a high-speed revolution, and can be structured into a large system.